When Grissom goes to enter the underground compound he only has his flashlight on his belt (on his back). What happened to the canteen he was wearing when he started? In later scenes inside the compound, he has it back on.

In the scene showing the meteor shower we can estimate five meteors per second (300 per minute) The actual maximum rate of the Orionids is 15 per minute or one every four seconds. A less than impressive shower from Comet Halley's particles.

Grissom looks up at a meteor shower he identifies as the Orionid shower. The camera shows a sky scene with the constellation Orion in the background, and a number of meteor trails moving from left to right across the star formation. This is dead wrong. Meteor showers are named for the region of the sky they appear to be coming from, e.g., Leonid (Leo), Perseid (Perseus). The meteor trails should appear to be coming straight at the viewer from Orion, not crossing it.

When Catherine finds the bowl full of burnt letters, Grissom tries to photograph the bowl in the state the cult members left it in. However, she rifled through and disturb the scene before he takes the pictures.

Grissom: The methodology here appears to be similar to the Heavens Gate Cult in California several years ago. They committed mass suicide to shed their Earthly bodies and hitch a ride on the spaceship hidden in the tail of a Hale-Bopp comet.